The present invention relates to anti-lock braking systems and in particular to circuitry for sensing, analyzing, and generating signals for indicating and/or modifying the response of an anti-lock braking system in response to detected faults in the system.
Anti-lock braking systems are well known. Early anti-lock braking systems were substantially mechanical. Such systems have now progressed to become sophisticated devices which can manage the application of braking forces with great speed, precision, and adaptability to provide substantially increased braking control under varying driving and road conditions. Increasing demand for safety and performance, coupled with the now proven effectiveness of such systems, renders the widespread application of such systems imminent.
Such systems remain, however, relatively expesive. There therefore continues to exist a need to reduce the complexity and corresponding cost of such systems while simultaneously maintaining a high level of reliability and safety. Even the finest components may experience failures as a result of wear, abuse, or damage. There therefore exists a need to provide anti-lock braking systems with means which will enable the system to defect and analyze component failures and to modify operation of the system to provide maximum available operation of the braking system in the event of a failure and to provide both the system and operator with a warning of the existence and nature of any such failure.
Broadly, the present invention is a failure mode detection system for use in an anti-lock braking system which comprises a network of fluid-level and fluid pressure responsive switches and logic circuitry connected to detect and analyze operating parameters of the adaptive braking system and generate a plurality of output signals for indicating and/or modifying operation of the braking system on the basis of detected failures therein.
The anti-lock braking system includes a master cylinder having a primary and a secondary chamber, and a power booster means which includes a pump and an accumulator for generating pressurized braking fluid. An electronic control system generates brake pressure control signals in response to predetermined operating parameters of the vehicle such as wheel speed, wheel acceleration, and the like. Modulating valve means respond to the control signals to control the level of braking pressure to provide optimum braking of the vehicle wheels. One such system described commonly in assigned co-pending U.S. patent application Ser. No. 789,203, filed Oct. 18, 1985 discloses an anti-lock bracking system modulating valve configuration wherein a three-way isolation valve normally connects each front wheel cylinder of the braking system and each rear wheel cylinder of the braking system to the primary and secondary chambers of the master cylinder, respectively. A normally closed build valve and a normally closed decay valve have a common fluid connection which is connected to the wheel cylinder or cylinders through the associated isolation valve.
The failure detection circuit of the present invention includes a first pressure differential switch connected between the primary and secondary chambers of the master cylinder, and a second differential pressure switch connected between either the primary or secondary chamber of the master cylinder, and the power booster boost pressure chamber. A pressure switch and fluid level switch may also be connected to the booster and accummulator and the reservoir to respond to the accumulator pressure and reservoir fluid level, respectively. Each of the switches is operable to operate from a normal to an operated state. A logic circuit is connected to the switches to generate output signals in response to predetermined operating combinations of the switches. Specific combinations of operation of the switches are correlated to determine failures in the systems such as, for example, pump failure, gassed brake lines, fluid leaks, and the like.
It is therefore an object of the invention to provide a system for identifying failure modes in an adaptive braking system.
It is another object of the invention to provide such a system incorporating a network of pressure responsive switches for detecting key operating parameters of the adaptive braking system.
Another object of the invention is to provide such a system which incorporates a logic circuit for analyzing operating combinations of the pressure switches.
Still another object of the invention is to provide such a system which generates control signals for modifying operation of the system in response to determined failure modes.
Still another object of the invention is to provide such a system which can provide detection, analysis, indication, and response to failure modes with a high level of reliability and minimum hardware.